Re: Surface scum

>One other thing, there are little (< 1mm) "fleas" that I can see
>jumping on the scum patches. Could these little cretins be
>responsible?
These insects are called springtails, of the order Collembola. There
are several families. They live on the water's surface, and probably
feed on the surface scum, along with plant debris. A good general
reference on this topic is "Fresh-water Invertebrates of the United
States" by Robert W. Pennak.
Surface scum is primarily composed of water-insoluble organic
compounds (proteins, fats, aromatics, etc) from fish food, and/or from
the decay of plant and animal matter in your aquarium. As the scum is
both water-insoluble and lighter than water, it floats. Secondarily,
other things can colonize the scum (presumably while feeding on it),
such as bacteria, fungi, and, of course, springtails.